The invention relates to a tension device for straining a threaded bolt by a pull on its threaded end portion, with a one-part or multi-part housing having at least one piston movable therein in the longitudinal direction and connectable to a hydraulic supply, with a supporting tube which is arranged as a prolongation of the housing and discharges the tension forces acting in the housing to a base surrounding the threaded bolt, and with a pull nut which can be fastened by means of thread engagement on a threaded end portion of the threaded bolt and which is supported in the longitudinal direction, by means of a pressure face, against a pressure-transmission face formed on the piston.
In as bolt tension device, such as is known, for example, from DE 43 41 707 A1, the hydraulic piston and the tension cylinder has to be pressed back into its lower initial position again after the conclusion of the tensioning process and therefore after pressure relief has occurred. This is troublesome, above all in the case of frequent or recurring tensioning processes, and results in loss of time until the tension device is prepared for the next tensioning process.
The object of the invention, therefore, is, by means of measures which can be implemented on the tension device at a low outlay in assembly terms, to arrive at an automatic piston return, so that, after the end of the respective tensioning process, the piston does not first have to be moved back into its initial position again by the application of force.